I dont understand how the insert function mechanism will be does someone get it(Having an array of linked lists as chaining should be used)?

Question

I have created an insert function that adds a students id,first name,last name and email in an array of linked list. I should create another function that checks if a certain student is available and update his email, but I don't know where to start with that function

HEADER FILE

#pragma once
#include <iostream>
#include <string>
using namespace std;
class HashTable
{
private:
    struct HashNode
    {
        string key;
        string value;
        HashNode* next;
    };
    HashNode* table[100];
    int currentSize;
    int maxSize;
public:
    HashTable(int x);
    void insert(string ID, string firstName, string lastName, string email);
    bool update(string ID, string newEmail);
};

CPP FILE

HashTable::HashTable(int x)
{
    maxSize = x;
};


 void HashTable::insert(string ID, string firstName, string lastName, string email)
{
    HashNode x;
    x.key = ID;
    x.value = firstName + " " + lastName + " " + email;
    int index = hash(x.key);
    if (*(table + index) == NULL)
    {
        *(table + index) = new HashNode;
        (*(table + index))->key = x.key;
        (*(table + index))->value = x.value;
        (*(table + index))->next = NULL;
    }
    else
    {
        HashNode* temp = *(table + index);
        while (temp->next != NULL)
            temp = temp->next;
        HashNode* newNode = new HashNode;
        newNode->key = x.key;
        newNode->value = x.value;
        newNode->next = NULL;
        temp->next = newNode;
        temp = NULL;
        newNode = NULL;
    }
    currentSize++;
};

Answer 1

1. You should store firstName, lastName and email as three separate string fields in HashNode instead of concatenating them in insert. That will save you numerous headaches.

2. In update function, you need to scan the linked list the student was (or could be) added to; that is, that starting at table[hash(ID)] (btw, table[index] is the same as *(table + index), at least for pointers [arrays are often treated as pointers in C and C++]). You need to find the node having the key you look for (if any), and update its email.